The present invention is related in general to communication systems, and, more particularly, to an improved method and system for retransmitting data packets in a communication system having variable data rates.
Standards bodies such as the International Standards Organization (ISO) have adopted a layered approach for the reference model of a communication subsystem. The complete communication subsystem is broken down into a number of layers, each of which performs a well-defined function in the context of the overall communication subsystem. It operates according to a defined protocol by exchanging messages,. both user data and additional control information, with a corresponding peer layer in a remote system. Each layer has a well-defined interface between itself and the layer immediately above and below. Consequently, the implementation of a particular protocol layer is independent of all other layers. The function of each layer is specified formally as a protocol that defines the set of rules and conventions used by the layer to communicate with a similar peer layer in another (remote) system. Each layer provides a defined set of services to the layer immediately above. It also uses the services provided by the layer immediately below it to transport the message units associated with the protocol to the remote peer layer.
Communication systems, such as Code Division Multiple Access (CDMA) systems, communicate messages between infrastructure equipment and subscriber or mobile units. As used herein, a forward message refers to a message generated by cellular infrastructure equipment and transmitted for reception by a mobile communication unit, and a reverse message refers to a message generated by a mobile communication unit, such as a mobile cellular phone.
At the most basic level, cdma2000 provides protocols and services that correspond to the bottom two layers of the ISO/OSI Reference Model (i.e., Layer 1xe2x80x94the Physical Layer, and Layer 2xe2x80x94the Link Layer) according to the general structure specified by the ITU for IMT-2000 systems. In cdma2000, a generalized multi-media service model is supported. This allows a combination of voice, packet data, and circuit data services to be operating concurrently (within the limitations of the air interface system capacity). Cdma2000 also includes a Quality of Service (QOS) control mechanism to balance the varying QOS requirements of multiple concurrent services.
One problem associated with the combination of voice, packet data, and circuit data services operating concurrently is the ability to maintain a high data rate connection at a required fixed error rate over a channel of varying quality. In addition, maximizing system capacity when high data rate channels are active presents another problem. Consequently, a need exists for a method and system for retransmitting data packets in a communication system having variable data rates, wherein data rates for high data rate channels are automatically shifted up or down based on a predetermined metric.